Colloidal Stability and Precipitation of Lipids in the Artificial and Human Bile in the Presence of Cations of Higher Valency

The intrinsic stability of human bile as well as the stability of model and natural bile in different salt environments were studied. The results suggested that irrespective of its cholesterol content, human bile was unstable and exhibited spontaneous precipitation of its three major components, cholesterol, phospholipids and bile salts. The extent of precipitation of each component varied from sample to sample. Salts imparted instability to the bile and cations of higher valancy were more effective. Multivalent cation, Ca⁺⁺, Mg⁺⁺ and Fe⁺⁺⁺ caused partial precipitation of all the three components of the model as well as the natural bile. The multivalent protein protamine sulphate was also a much effective precipitant. The precipitation by the electrolytes followed the Hardy-Shulze valency rule observed for hydrophobic colloids according to which the power of precipitation by an electrolyte depends on its ion carrying charge opposite in sign to that of the colloid. The effectivity followed the order: protamine sulphate>FeCl^-₃₂>MgCl₂>CaCl₂>NaCl. Washing of the precipitates by either water or isotonic saline in the case of model bile and by diluted bile in the case of human bile resulted resolubilisation of a part of the phospholipids and bile salts. All these results advocated colloid chemical nature of bile. They also suggested that the micro components of the human bile give some natural protection against precipitation.